Expander

ABSTRACT

An expander is provided in which a rotor ( 22 ) is rotated by supplying high-temperature, high-pressure steam to an expansion chamber ( 43 ) defined between a piston ( 42 ) and a cylinder sleeve ( 41 ) so that the piston ( 42 ) pushes a swash plate ( 31 ), and sliding surfaces of the piston ( 42 ) and the cylinder sleeve ( 41 ) are lubricated with oil supplied via an oil hole ( 32   c ). The piston ( 42 ) includes a top part ( 63 ) that is exposed to high-temperature, high-pressure steam within the expansion chamber ( 43 ), an end part ( 61 ) that abuts against the swash plate ( 31 ), and a middle part ( 62 ) that is present between the end part ( 61 ) and the top part ( 63 ) and is in sliding contact with the cylinder sleeve ( 41 ), the top part ( 63 ) being formed from a heat-resistant and corrosion-resistant material, the end part ( 61 ) being formed from a material having high surface pressure resistance, and the middle part ( 62 ) being formed from a material having high abrasion resistance. This enables the durability of the piston ( 42 ) of an axial piston cylinder type expander to be improved.

FIELD OF THE INVENTION

The present invention relates to an expander that includes a casing, a rotor rotatably supported in the casing, and an axial piston cylinder group arranged annularly in the rotor so as to surround the axis of the rotor, the rotor being rotated by supplying high-temperature, high-pressure steam to expansion chambers defined between pistons and cylinder sleeves of the axial piston cylinder group, and sliding surfaces of the piston and the cylinder sleeve being lubricated with oil.

BACKGROUND ART

Such an expander has been proposed by the present applicant in Japanese Patent Application No. 2001-61424. This expander is used in a Rankine cycle system, and includes an axial piston cylinder group arranged annularly in a rotor so as to surround the axis of the rotor, and lubrication of a section where a piston and a cylinder sleeve slide against each other is carried out by oil, which is separate from the steam (water) that is the working medium of the expander.

A top part of the piston of such an expander is exposed to high-temperature, high-pressure steam supplied to an expansion chamber of the cylinder sleeve, and is not only easily oxidized, but also might be corroded by contact with water formed by condensation of the steam. An end part of the piston might be damaged by a large load due to abutment against a swash plate. A middle part of the piston, which slides against the cylinder sleeve, is lubricated with oil, but if steam that has leaked from the expansion chamber of the cylinder sleeve condenses to become water and adheres to the sliding surfaces, the oil will be contaminated by the water, it becomes difficult to maintain an oil film, and abnormal wear might occur.

However, in the above-mentioned conventional arrangement, since the top part, the end part, and the middle part of the piston are made integrally of identical materials, it is difficult to completely satisfy the requirements of each part for heat resistance, corrosion resistance, high surface pressure resistance, abrasion resistance, etc.

DISCLOSURE OF INVENTION

The present invention has been achieved under the above-mentioned circumstances, and it is an object thereof to improve the durability of a piston of an axial piston cylinder type expander.

In order to attain this object, in accordance with a first aspect of the present invention, there is proposed an expander that includes a casing, a rotor rotatably supported in the casing, and an axial piston cylinder group arranged annularly in the rotor so as to surround the axis of the rotor, the rotor being rotated by supplying high-temperature, high-pressure steam to an expansion chamber defined between a piston and a cylinder sleeve of the axial piston cylinder group, and sliding surfaces of the piston and the cylinder sleeve being lubricated with oil, characterized in that the piston includes a top part that is exposed to high-temperature, high-pressure steam within the expansion chamber, an end part that abuts against a swash plate, and a middle part that is present between the end part and the top part and is in sliding contact with the cylinder sleeve, the top part being formed from a heat-resistant and corrosion-resistant material, the end part being formed from a material having high surface pressure resistance, and the middle part being formed from a material having high abrasion resistance.

In accordance with this arrangement, with regard to the expander piston that includes the end part, the top part, and the middle part, the top part, which is exposed to high-temperature, high-pressure steam supplied to the expansion chamber, is formed from the heat-resistant and corrosion-resistant material, and it is therefore possible to prevent the top part from being oxidized due to heat and from being corroded by contact with water from the liquefaction of steam. Furthermore, since the end part of the piston, which abuts against the swash plate, is formed from the material having high surface pressure resistance, it is possible to prevent the end part from being damaged by a strong surface pressure applied by the swash plate. Moreover, since the middle part of the piston, which is in sliding contact with the cylinder sleeve, is formed from the material having high abrasion resistance, even if water from the condensation of steam contaminates the oil on the sliding surfaces and degrades the lubrication performance, it is possible to prevent the occurrence of abnormal wear.

Furthermore, in accordance with a second aspect of the present invention, in addition to the first aspect, there is proposed an expander wherein a heat-insulating space is provided between the top part and the middle part.

In accordance with this arrangement, since the heat-insulating space is provided between the top part and the middle part of the piston, it is possible to suppress escape, from the top part to the cylinder sleeve via the middle part, of the heat of the high-temperature, high-pressure steam that has been supplied to the expansion chamber, thereby enabling degradation of the thermal efficiency of the expander to be minimized.

Moreover, in accordance with a third aspect of the present invention, in addition to the first or second aspect, there is proposed an expander wherein a hollow space is formed in the middle part, an oil ring channel formed on an outer peripheral face of the top part communicates with the hollow space via a first oil hole, and a small diameter part formed on an outer peripheral face of the middle part communicates with the hollow space via a second oil hole.

In accordance with this arrangement, since the hollow space is formed in the middle part of the piston, not only is it possible to reduce the weight of the piston, but it is also possible to suppress the escape of heat from the piston to the cylinder sleeve due to the hollow space functioning as a heat-insulating layer, thus minimizing degradation of the thermal efficiency of the expander. Furthermore, since the hollow space of the piston communicates with the bottom of the oil ring channel formed in the top part via the first oil hole and with the small diameter part formed in the middle part via the second oil hole, it is possible to discharge, into the small diameter part of the piston via the second oil hole, the oil recovered in the hollow space from the oil ring channel via the first oil hole, and provide the oil for lubrication of sliding surfaces of the piston and the cylinder sleeve.

Oil holes 63 c and 62 c of an embodiment correspond to the first oil hole and the second oil hole respectively of the present invention.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 to FIG. 13 show one embodiment of the present invention;

FIG. 1 is a vertical sectional view of an expander,

FIG. 2 is a sectional view along line 2-2 in FIG. 1,

FIG. 3 is a view from arrowed line 3-3 in FIG. 1,

FIG. 4 is an enlarged view of part 4 in FIG. 1,

FIG. 5 is an enlarged view of part 5 in FIG. 1,

FIG. 6 is an exploded perspective view of a rotor,

FIG. 7 is a sectional view along line 7-7 in FIG. 4,

FIG. 8 is a sectional view along 8-8 in FIG. 4,

FIG. 9 is an enlarged view of part 9 in FIG. 4,

FIG. 10 is a sectional view along line 10-10 in FIG. 5,

FIG. 11 is a sectional view along line 11-11 in FIG. 5,

FIG. 12 is a sectional view along line 12-12 in FIG. 5, and

FIG. 13 is a sectional view along line 13-13 in FIG. 5.

BEST MODE FOR CARRYING OUT THE INVENTION

One embodiment of the present invention is explained below with reference to the attached drawings.

As shown in FIG. 1 to FIG. 9, an expander M of this embodiment is used in, for example, a Rankine cycle system, and converts the thermal energy and the pressure energy of high-temperature, high-pressure steam as a working medium into mechanical energy and outputs it. A casing 11 of the expander M is formed from a casing main body 12, a front cover 15 joined via a seal 13 to a front opening of the casing main body 12 by a plurality of bolts 14, a rear cover 18 joined via a seal 16 to a rear opening of the casing main body 12 by a plurality of bolts 17, and an oil pan 21 joined via a seal 19 to a lower opening of the casing main body 12 by a plurality of bolts 20.

A rotor 22 disposed rotatably around an axis L extending in the fore-and-aft direction in the center of the casing 11 has a front part thereof supported by a ball bearing 23 provided in the front cover 15 and a rear part thereof supported by a ball bearing 24 provided in the casing main body 12. A swash plate holder 28 is fitted in a rear face of the front cover 15 via two seals 25 and 26 and a knock pin 27, and fixed thereto via a plurality of bolts 29, and a swash plate 31 is rotatably supported by the swash plate holder 28 via an angular ball bearing 30. The axis of the swash plate 31 is inclined relative to the axis L of the rotor 22, and the angle of inclination is fixed.

The rotor 22 includes an output shaft 32 supported by the front cover 15 via the ball bearing 23, three sleeve support flanges 33, 34, and 35 formed integrally with a rear part of the output shaft 32 via cutouts 57 and 58 having predetermined widths (see FIG. 4 and FIG. 9), a rotor head 38 that is joined by a plurality of bolts 37 to the rear sleeve support flange 35 via a metal gasket 36 and supported by the casing main body 12 via the ball bearing 24, and a heat-insulating cover 40 that is fitted over the three sleeve support flanges 33, 34, and 35 from the front and joined to the front sleeve support flange 33 by a plurality of bolts 39.

Sets of five sleeve support holes 33 a, 34 a, and 35 a are formed in the three sleeve support flanges 33, 34, and 35 respectively at intervals of 72° around the axis L, and five cylinder sleeves 41 are fitted into the sleeve support holes 33 a, 34 a, and 35 a from the rear. A flange 41 a is formed on the rear end of each of the cylinder sleeves 41, and axial positioning is carried out by abutting this flange 41 a against the metal gasket 36 while fitting the flange 41 a into a step 35 b formed in the sleeve support holes 35 a of the rear sleeve support flange 35 (see FIG. 9). A piston 42 is slidably fitted within each of the cylinder sleeves 41, the front end of the piston 42 abutting against a dimple 31 a formed on the swash plate 31, and a steam expansion chamber 43 is defined between the rear end of the piston 42 and the rotor head 38.

An oil passage 32 a is formed so as to extend on the axis L within the output shaft 32, which is integral with the rotor 22, and the front end of the oil passage 32 a branches in a radial direction and communicates with an annular channel 32 b on the outer periphery of the output shaft 32. An oil passage blocking member 45 is screwed into the inner periphery of the oil passage 32 a via a seal 44 at a radially inner position of the middle sleeve support flange 34 of the rotor 22, and a plurality of oil holes 32 c extending radially outward from the oil passage 32 a in the vicinity of the oil passage blocking member 45 open on the outer periphery of the output shaft 32.

A trochoidal oil pump 49 is disposed between a recess 15 a provided in a front face of the front cover 15 and a pump cover 48 fixed via a seal 46 to the front face of the front cover 15 by a plurality of bolts 47, and includes an outer rotor 50 that is rotatably fitted in the recess 15 a, and an inner rotor 51 that is fixed to the outer periphery of the output shaft 32 and meshes with the outer rotor 50. An internal space of the oil pan 21 communicates with an intake port 53 of the oil pump 49 via an oil pipe 52 and an oil passage 15 b of the front cover 15, and a discharge port 54 of the oil pump 49 communicates with the annular channel 32 b of the output shaft 32 via an oil passage 15 c of the front cover 15.

The piston 42, which is slidably fitted into the cylinder sleeve 41, is formed from an end part 61, a middle part 62, and a top part 63. The end part 61 is a member having a spherical part 61 a that abuts against the dimple 31 a of the swash plate 31, and is joined by welding to the forward end of the middle part 62. The middle part 62 is a cylindrical member having a large volume hollow space 62 a; an outer peripheral part of the middle part 62 close to the top part 63 has a small diameter part 62 b whose diameter is slightly reduced, a plurality of oil holes 62 c are formed so as to run radially through the small diameter part 62 b, and a plurality of spiral oil channels 62 d are formed in an outer peripheral part that is present forward of the small diameter part 62 b. The top part 63 faces the expansion chamber 43 and is formed integrally with the middle part 62, and a heat-insulating space 65 is formed between a dividing wall 63 a formed on an inner face of the top part 63 and a cover member 64 fitted into and welded to a rear end face of the top part 63 (see FIG. 9). Two compression rings 66 and one oil ring 67 are mounted on the outer periphery of the top part 63, and an oil ring channel 63 b into which the oil ring 67 is fitted communicates with the hollow space 62 a of the middle part 62 via a plurality of oil holes 63 c.

The end part 61 and the middle part 62 of the piston are made of high-carbon steel, and the top part 63 is made of stainless steel; among these, the end part 61 is subjected to induction hardening, whereas the middle part 62 is subjected to hardening. As a result, high surface pressure resistance can be imparted to the end part 61, which abuts against the swash plate 31 at a high surface pressure, abrasion resistance can be imparted to the middle part 62, which is in sliding contact with the cylinder sleeve 41 under severe lubrication conditions, and heat resistance and corrosion resistance can be imparted to the top part 63, which faces the expansion chamber 43 and is exposed to high temperature and high pressure.

An annular channel 41 b is formed on the outer periphery of a middle part of the cylinder sleeve 41 (see FIG. 6 and FIG. 9), and a plurality of oil holes 41 c are formed in the annular channel 41 b. Regardless of where rotationally the cylinder sleeve 41 is mounted, the oil holes 32 c formed in the output shaft 32 and oil holes 34 b formed in the middle sleeve support flange 34 of the rotor 22 (see FIG. 4 and FIG. 6) communicate with the annular channel 41 b. A space 68 formed between the heat-insulating cover 40 and the front and rear sleeve support flanges 33 and 35 of the rotor 22 communicates with the internal space of the casing 11 via oil holes 40 a formed in the heat-insulating cover 40 (see FIG. 4 and FIG. 7).

An annular cover member 69 is welded to the front, or expansion chamber 43 side, of the rotor head 38, which is joined to the rear face of the front sleeve support flange 33 of the rotor 22 by the bolts 37, and an annular heat-insulating space 70 is defined at the back, or rear face of the cover member 69 (see FIG. 9). The rotor head 38 is positioned rotationally relative to the rear sleeve support flange 35 by a knock pin 55.

The five cylinder sleeves 41 and the five pistons 42 form an axial piston cylinder group 56 of the present invention.

The structure of a rotary valve 71 for the supply and discharge of steam to and from the five expansion chambers 43 of the rotor 22 is now explained with reference to FIG. 5, and FIG. 10 to FIG. 13.

As shown in FIG. 5, the rotary valve 71, which is disposed along the axis L of the rotor 22, includes a valve main body 72, a stationary valve plate 73, and a movable valve plate 74. The movable valve plate 74 is fixed to a rear face of the rotor 22 by a bolt 76 screwed into the oil passage blocking member 45 (see FIG. 4) while being positioned in the rotational direction by a knock pin 75. The bolt 76 also has the function of fixing the rotor head 38 to the output shaft 32.

As is clear from FIG. 5, the stationary valve plate 73, which abuts against the movable valve plate 74 via flat sliding surfaces 77, is fixed to the center of a front face of the valve main body 72 by one bolt 78, and also to an outer peripheral part of the valve main body 72 by an annular fixing ring 79 and a plurality of bolts 80. During this process, a step 79 a formed on the inner periphery of the fixing ring 79 is press-fitted around the outer periphery of the stationary valve plate 73 so as to be fitted in a socket-and-spigot type, and a step 79 b formed on the outer periphery of the fixing ring 79 is fitted in a socket-and-spigot type around the outer periphery of the valve main body 72, thereby ensuring that the stationary valve plate 73 is coaxial with the valve main body 72. A knock pin 81 is disposed between the valve main body 72 and the stationary valve plate 73, and determines the position of the stationary valve plate 73 in the rotational direction.

When the rotor 22 rotates, the movable valve plate 74 and the stationary valve plate 73 therefore rotate relative to each other on the sliding surfaces 77 in a state in which they are in intimate contact with each other. The stationary valve plate 73 and the movable valve plate 74 are made of a material having excellent durability, such as carbon or a ceramic, and the durability can be further improved by providing or coating the sliding surfaces 77 with a member having heat resistance, lubricating properties, corrosion resistance, and abrasion resistance.

The valve main body 72, which is made of stainless steel, is a stepped cylindrical member having a large diameter part 72 a and a small diameter part 72 b; outer peripheral faces of the large diameter part 72 a and the small diameter part 72 b are slidably fitted in the axial L direction into circular cross-section support faces 18 a and 18 b of the rear cover 18 via seals 82 and 83 respectively, and positioned in the rotational direction by fitting a pin 84 implanted in an outer peripheral face of the valve main body 72 into a cutout 18 c formed in the axial L direction in the rear cover 18. A plurality of preload springs 85 are supported in the rear cover 18 so as to surround the axis L, and the valve main body 72, which has a step 72 c between the large diameter part 72 a and the small diameter part 72 b pushed by these preload springs 85, is biased forward so as to put the sliding surfaces 77 of the stationary valve plate 73 and the movable valve plate 74 in intimate contact.

A steam supply pipe 86 connected to a rear face of the valve main body 72 communicates with the sliding surfaces 77 via a first steam passage P1 formed in the interior of the valve main body 72 and a second steam passage P2 formed in the stationary valve plate 73. A steam discharge chamber 88 sealed by a seal 87 is formed between the casing main body 12, the rear cover 18, and the rotor 22, and this steam discharge chamber 88 communicates with the sliding surfaces 77 via sixth and seventh steam passages P6 and P7 formed in the interior of the valve main body 72 and a fifth steam passage P5 formed in the stationary valve plate 73. Provided on surfaces where the valve main body 72 and the stationary valve plate 73 are joined are a seal 89 surrounding a part where the first and second steam passages P1 and P2 are connected to each other and a seal 90 surrounding a part where the fifth and sixth steam passages P5 and P6 are connected to each other.

Five third steam passages P3 disposed at equal intervals so as to surround the axis L run through the movable valve plate 74, and opposite ends of five fourth steam passages P4 formed in the rotor 22 so as to surround the axis L communicate with the third steam passages P3 and the expansion chambers 43. The part of the second steam passage P2 opening on the sliding surface 77 is circular, whereas the part of the fifth steam passage P5 opening on the sliding surface 77 has an arc shape with the axis L as its center.

The operation of the expander M of this embodiment having the above-mentioned arrangement is now explained.

High-temperature, high-pressure steam generated by heating water in an evaporator reaches the sliding surfaces 77 of the stationary valve plate 73 with the movable valve plate 74 from the steam supply pipe 86 via the first steam passage P1 formed in the valve main body 72 of the rotary valve 71 and the second steam passage P2 formed in the stationary valve plate 73, which is integral with the valve main body 72. The second steam passage P2 opening on the sliding surface 77 communicates momentarily during a predetermined intake period with the corresponding third steam passage P3 formed in the movable valve plate 74, which rotates integrally with the rotor 22, and the high-temperature, high-pressure steam is supplied, via the fourth steam passage P4 formed in the rotor 22, from the third steam passage P3 to the expansion chamber 43 within the cylinder sleeve 41.

Even after the communication between the second steam passage P2 and the third steam passage P3 has been blocked due to rotation of the rotor 22, the high-temperature, high-pressure steam expands within the expansion chamber 43 and causes the piston 42 fitted in the cylinder sleeve 41 to be pushed forward from top dead center toward bottom dead center, and the end part 61 at the front end of the piston 42 pushes against the dimple 31 a of the swash plate 31. As a result, the reaction force that the pistons 42 receive from the swash plate 31 gives a rotational torque to the rotor 22. For each one fifth of a revolution of the rotor 22, the high-temperature, high-pressure steam is supplied into a fresh adjoining expansion chamber 43, thus continuously rotating the rotor 22.

While the piston 42, having reached bottom dead center accompanying rotation of the rotor 22, retreats toward top dead center by being pushed by the swash plate 31, the low-temperature, low-pressure steam pushed out of the expansion chamber 43 is discharged into the steam discharge chamber 88 via the fourth steam passage P4 of the rotor 22, the third steam passage P3 of the movable valve plate 74, the sliding surfaces 77, the arc-shaped fifth steam passage P5 of the stationary valve plate 73, and the sixth and seventh steam passages P6 and P7 of the valve main body 72, and is supplied therefrom into a condenser.

The oil pump 49 provided on the output shaft 32 operates accompanying rotation of the rotor 22, and oil is taken in from the oil pan 21 via the oil pipe 52, the oil passage 15 b of the front cover 15, and the intake port 53, discharged from the discharge port 54, and supplied to a space between the cylinder sleeve 41 and the small diameter part 62 b formed in the middle part 62 of the piston 42 via the oil passage 15 c of the front cover 15, the oil passage 32 a of the output shaft 32, the annular channel 32 b of the output shaft 32, the oil holes 32 c of the output shaft 32, the annular channel 41 b of the cylinder sleeve 41, and the oil holes 41 c of the cylinder sleeve 41. A portion of the oil retained by the small diameter part 62 b flows into the spiral oil channels 62 d formed in the middle part 62 of the piston 42 and lubricates the surface that slides against the cylinder sleeve 41, and another portion of the oil lubricates surfaces of the compression rings 66 and the oil ring 67 provided at the top part 63 of the piston 42 that slide against the cylinder sleeve 41.

Since water formed in the expansion chamber 43 by condensation of a portion of the supplied high-temperature, high-pressure steam inevitably enters between the sliding surfaces of the cylinder sleeve 41 and the piston 42 and contaminates the oil, the lubrication conditions of the sliding surfaces are severe, but by supplying a necessary amount of oil directly to the sliding surfaces of the cylinder sleeve 41 and the piston 42 from the oil pump 49 via the interior of the output shaft 32, it is possible to maintain a sufficient oil film, thereby ensuring the lubrication performance and enabling the dimensions of the oil pump 49 to be reduced.

Oil scraped off the surface of the cylinder sleeve 41 that the piston 42 slides against by the oil ring 67 flows from the oil holes 63 c formed in the base of the oil ring channel 63 b into the hollow space 62 a within the piston 42. The hollow space 62 a communicates with the interior of the cylinder sleeve 41 via the plurality of oil holes 62 c running through the middle part 62 of the piston 42, and the interior of the cylinder sleeve 41 communicates with the annular channel 41 b on the outer periphery of the cylinder sleeve 41 via the plurality of oil holes 41 c. Although the surroundings of the annular channel 41 b are covered by the middle sleeve support flange 34 of the rotor 22, since the oil hole 34 b is formed in the sleeve support flange 34, the oil within the hollow space 62 a of the piston 42 is biased radially outward due to centrifugal force, discharged to the space 68 within the heat-insulating cover 40 via the oil hole 34 b of the sleeve support flange 34, and returned therefrom to the oil pan 21 via the oil holes 40 a of the heat-insulating cover 40. During this process, since the oil hole 34 b is positioned toward the axis L relative to the radially outer edge of the sleeve support flange 34, the oil that is present radially outside the oil hole 34 b is retained in the hollow space 62 a of the piston 42 by centrifugal force.

In this way, the oil retained in the hollow space 62 a within the piston 42 and the oil retained in the small diameter part 62 b on the outer periphery of the piston 42 are supplied from the small diameter part 62 b to the top part 63 side during an expansion stroke in which the volume of the expansion chamber 43 increases, and are supplied from the small diameter part 62 b to the end part 61 side during a compression stroke in which the volume of the expansion chamber 43 decreases, and it is therefore possible to ensure reliable lubrication over the entire axial region of the piston 42. Furthermore, as a result of the oil flowing within the hollow space 62 a of the piston 42, the heat of the top part 63, which is exposed to high-temperature, high-pressure steam, is transmitted to the end part 61, which has a low temperature, and it is thus possible to avoid the temperature of the piston 42 increasing locally.

When high-temperature, high-pressure steam is supplied from the fourth steam passage P4 to the expansion chamber 43, since the heat-insulating space 65 is formed between the middle part 62 and the top part 63 of the piston 42, which faces the expansion chamber 43, and the heat-insulating space 70 is formed in the rotor head 38, which faces the expansion chamber 43, it is possible to minimize the escape of heat from the expansion chamber 43 to the piston 42 and the rotor head 38, thereby contributing to an improvement in the performance of the expander M. Furthermore, since the large volume hollow space 62 a is formed within the piston 42, not only is it possible to reduce the weight of the piston 42, but also it is possible to reduce the heat capacity of the piston 42, thereby enabling the escape of heat from the expansion chamber 43 to be suppressed yet more effectively.

Since the expansion chamber 43 is sealed by interposing the metal gasket 36 between the rear sleeve support flange 35 and the rotor head 38, in comparison with a case in which the expansion chamber 43 is sealed via a thick annular seal, unnecessary volume around the seal can be reduced, thus ensuring that the expander M has a large volume ratio (expansion ratio) and thereby improving the thermal efficiency, which enables the output to be increased. Moreover, since the cylinder sleeve 41 is formed separately from the rotor 22, the material of the cylinder sleeve 41 can be selected without being restricted by the material of the rotor 22, while taking into consideration the thermal conductivity, heat resistance, strength, abrasion resistance, etc., and, moreover, it is possible to replace only a worn or damaged cylinder sleeve 41, which is economical.

Furthermore, since the outer peripheral face of the cylinder sleeve 41 is exposed through the two cutouts 57 and 58 formed circumferentially in the outer peripheral face of the rotor 22, not only is it possible to reduce the weight of the rotor 22, but it is also possible to reduce the heat capacity of the rotor 22, thereby improving the thermal efficiency and, moreover, the cutouts 57 and 58 function as a heat-insulating space, thus suppressing the escape of heat from the cylinder sleeve 41. Furthermore, since the outer peripheral part of the rotor 22 is covered by the heat-insulating cover 40, it is possible to suppress the escape of heat from the cylinder sleeve 41 yet more effectively.

Since the rotary valve 71 supplies and discharges steam to and from the axial piston cylinder group 56 via the flat sliding surfaces 77 between the stationary valve plate 73 and the movable valve plate 74, it is possible to prevent the leakage of steam effectively. This is because the flat sliding surfaces 77 can easily be machined with high precision, and control of the clearance is easy compared with cylindrical sliding surfaces. Moreover, since a surface pressure is generated on the sliding surfaces 77 of the stationary valve plate 73 and the movable valve plate 74 by applying a preset load to the valve main body 72 by means of the plurality of preload springs 85, it is possible to suppress the leakage of steam past the sliding surfaces 77 yet more effectively.

Furthermore, since the valve main body 72 of the rotary valve 71 is made of stainless steel, which has a large coefficient of thermal expansion, and the stationary valve plate 73 fixed to the valve main body 72 is made of carbon or a ceramic, which has a small coefficient of thermal expansion, there is the possibility that the centering between the two might be displaced due to a difference in the coefficients of thermal expansion, but since the fixing ring 79 is fixed to the valve main body 72 by means of the plurality of bolts 80 in a state in which the step 79 a on the inner periphery of the fixing ring 79 is press-fitted over the outer periphery of the stationary valve plate 73 in a socket-and-spigot type fitting and the step 79 b on the outer periphery of the fixing ring 79 is press-fitted over the outer periphery of the valve main body 72 in a socket-and-spigot type fitting, it is possible to carry out precise centering of the stationary valve plate 73 relative to the valve main body 72 by the aligning action of the socket-and-spigot type fitting of the fixing ring 79 and prevent the timing of supply and discharge of steam from deviating, thereby preventing deterioration in the performance of the expander M. Moreover, it is possible to make the abutting surfaces of the stationary valve plate 73 and the valve main body 72 come into intimate and uniform contact by virtue of the securing force of the bolts 80, thereby suppressing the leakage of steam past the abutting surfaces.

Moreover, since the rotary valve 71 can be attached to and removed from the casing main body 12 merely by removing the rear cover 18 from the casing main body 12, the ease of maintenance operations such as repair, cleaning, and replacement can be greatly improved. Furthermore, although the rotary valve 71 through which the high-temperature, high-pressure steam passes reaches a high temperature, since the swash plate 31 and the output shaft 32, where lubrication by oil is required, are disposed on the opposite side of the rotor 22 to the rotary valve 71, degradation of the lubrication performance of the swash plate 31 and the output shaft 32 due to heating of the oil by the heat of the rotary valve 71, which reaches a high temperature, can be prevented. Moreover, the oil also exhibits the function of cooling the rotary valve 71, thus preventing overheating.

Although an embodiment of the present invention is explained above, the present invention can be modified in a variety of ways without departing from the spirit and scope thereof.

For example, the expander M is illustrated for a Rankine cycle system in the embodiment, but the expander M of the present invention can be applied to any other purpose.

Furthermore, the materials and procedures for a thermal treatment, surface treatment, etc. of the end part 61, the middle part 62, and the top part 63 of the piston 42 are not limited by the embodiment, and can be changed appropriately as long as desired properties can be maintained.

INDUSTRIAL APPLICABILITY

The expander of the present invention is suitable for application to a Rankine cycle system, but the present invention can be applied to an expander for any purpose as long as the thermal energy and the pressure energy of a high-temperature, high-pressure working medium is converted into mechanical energy and output. 

1. An expander comprising: a casing (11); a rotor (22) rotatably supported in the casing (11); and an axial piston cylinder group (56) arranged annularly in the rotor (22) so as to surround an axis (L) of the rotor; the rotor (22) being rotated by supplying high-temperature, high-pressure steam to an expansion chamber (43) defined between a piston (42) and a cylinder sleeve (41) of the axial piston cylinder group (56), and sliding surfaces of the piston (42) and the cylinder sleeve (41) being lubricated with oil; characterized in that that piston (42) comprises a top part (63) that is exposed to high-temperature, high-pressure steam within expansion chamber (43), an end part (61) that abuts against a swash plate (31), and a middle part (62) that is present between the end part (61) and the top part (63) and is in sliding contact with the cylinder sleeve (41), the top part (63) being formed from a heat-resistant and corrosion-resistant material, the end part (61) being formed from a material having high surface pressure resistance, and the middle part (62) being formed from a material having high abrasion resistance.
 2. The expander according to claim 1, wherein a heat-insulating space (65) is provided between the top part (63) and the middle part (62).
 3. The expander according to, claim 1 wherein a hollow space (62 a) is formed in the middle part (62), an oil ring channel (63 b) formed on an outer peripheral face of the top part (63) communicates with the hollow space (62 a) via a first oil hole (63 c), and a small diameter part (62 b) formed on an outer peripheral face of the middle part (62) communicates with the hollow space (62 a) via a second oil hole (62 c).
 4. The expander according to claim 2, wherein a hollow space (62 a) is formed in the middle part (62), an oil ring channel (63 b) formed on an outer peripheral face of the top part (63) communicates with the hollow space (62 a) via a first oil hole (63 c), and a small diameter part (62 b) formed on an outer peripheral face of the middle part (62) communicates with the hollow space (62 a) via a second oil hole (62 c). 